Abstract: T cells can be genetically modified to target tumors through the expression of a chimeric antigen receptor (CAR). Most notably, CAR T cells have demonstrated its clinical efficacy in hematologic malignancies with evident responses when targeting solid tumors. However, CAR T cells therapy also has the capacity to elicit expected and unexpected toxicities including cytokine release syndrome, neurologic toxicity, “on target/off tumor” recognition, and anaphylaxis. Theoretical toxicities include clonal expansion secondary to insertional oncogenesis, graft versus host disease, and off-target antigen recognition. Abrogating toxicity has become a critical step in the successful application of this emerging technology. To this end, we review the reported and theoretical toxicities of CAR T cells therapy and strategies to cope with it.